From my past Test Eng experience a typical cable test with automated cable testers ( e.g. CIRRUS) is 100mΩ max, with 1kV HiPot for any cable or harness.
Test time ~1s.
Hi Tony,
That sounds good too. I had time to test some of these thoroughly so i let them sit for a while in free air at room temperature to see how hot they would get and where they got hot if at all. The results surprised me because i had assumed that the more expensive and sturdy looking cords would be better overall, which i found not to be the case. After fixing that one end though (replacing it with a quality socket end) it works well now, because that was the weak point in the design. The wire itself was good because it was a heavy enough gauge to handle the current, it was just the poor design of the socket part that killed the whole design. If they improved that, this would be a really high quality extension cord without any need for modification.
One significant point that came up here though was that resistance itself may not be a property of the cord that tells us if the cord is good or not, assuming a set of randomly chosen cords. For a randomly chosen set of cords one cord might be ok with 100mOhm while the next may not be. That's because heat is depending on resistance, while temperature is dependent on both heat AND dissipation factor.
For example, take a 100mOhm resistor and run 10 amps though it, what power does it try to dissipate. As we all know, 10 squared is 100 and that times 0.1 is 10 watts. Spread that out over 100 square inches and the power density is only 0.1 watt per square inch, which might show a temperature rise of 5 degrees C. Contain that within 10 square inches and that's 1 watt per square inch which means the temperature can go as high as around 67 degrees C or so.
So it partly depends where that resistance is located, physically. If it is over the entire length, that's great, but if like in my cord it is mostly in the CONNECTOR which is small to begin with, it gets hot. Since the connector is also insulated, that means it is not very good at dissipating heat.
In a plant where cords of the same type are made that could be different because that 100mOhm shows that it is the same as other cords of the same make, and at least some of them were already tested more rigorously and found to have 100mOhm short term resistance. If they all have 100mOhm then they are probably good. But for a randomly chosen cord, we have to be more careful im sure you agree.